As of Mar 17, 2010 a minimal history is maintained for Recipes on ActiveState Code. The history of a recipe is available by clicking on the "Revision N" link in the "Other Information and Tasks" section of the recipe page sidebar. Note that because maintenance of history was only added after a certain date, Recipe code revisions before that date are not available.
The history facility was added primarily to support better conflict resolution for adding/editing/forking/updating of recipe code via the site's Recipes API. More details on this to follow.